Why patients on lithium need attention
A BNF case study that reminds pharmacists of the valuable role they have to play in preventing harm from lithium therapy
A 28-year-old woman with a history of mania presents with a repeat prescription for 28 days’ supply of Priadel M/R tablets 400mg od.
She complains that she is feeling weak and cold. She has recently become constipated and is experiencing heavy menstrual bleeding. Further conversation reveals that her blood was last tested by a psychiatric unit over seven months ago.
She does not display any symptoms of mania and has not had a relapse since her initial hospital admission. Her patient medication record shows that she has been taking Priadel for over a year. You decide to speak to her GP.
Which laboratory parameters will you ask the GP to measure?
According to the prescribing notes for lithium (section 4.2.3, BNF 60), long-term use of this drug has been associated with thyroid disorders, with women at greater risk of hypothyroidism than men. This patient’s symptoms should alert you to the possibility of lithium-induced hypothyroidism.
Because she is receiving long-term treatment with lithium, thyroid and renal function should be monitored every six months or more frequently if there is evidence of deterioration. Renal function should also be monitored more frequently if there are other risk factors, such as starting angiotensin-converting enzyme inhibitors, non-steroidal anti-inflammatory drugs or diuretics.
Serum lithium concentration should be monitored weekly on initiation of treatment or following dose changes, and every three months once levels are stable. If this patient is confirmed to be hypothyroid, the management of her mania will have to be reviewed.
If lithium-induced hypothyroidism is confirmed, an alternative treatment should be considered for her mania because the hypothyroidism is reversible if lithium is withdrawn. If continued treatment with lithium is essential, the patient should be treated with levothyroxine.
What should the target range be for this patient’s serum lithium concentration?
Because she is receiving lithium maintenance therapy, this patient’s serum lithium concentration should be at the lower end of the range of 0.4–1mmol/L for a sample taken 12 hours after the preceding dose. It is important to determine the optimum range for each individual patient.
Adapted from BNF 59 Community e-Update, an e-learning module produced by the Centre for Pharmacy Postgraduate Education (CPPE) and the British National Formulary.
BNF 60 Community e-Update is now available online
Citation: The Pharmaceutical Journal URI: 11049610
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